Need help!
Thread Starter
6th Gear
Joined: Apr 2021
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1985 C4 Engine issues running very sluggish
So I have a 1985 C4 with 110k on the books, she idles really rough, by that I mean it jumps around like crazy all the way down to 370rpm is the lowest we’ve recorded. When I go to give it gas it stalls out and dies, when it does run on the highway I’m getting a lot of misfires as in I can hear the pops in the exhaust from it. My oil pressure sensor is reading 80 on a cold start. Whenever I go to give it gas on the highway it builds up a lot of power but doesn’t send it anywhere the engine only gets louder and when I let my foot off the gas the car shoots forwards. I’ve replaced the fuel filter, spark plugs, and air filter so far, what else could I need to get her back to life.
Last edited by Moji; Apr 13, 2021 at 05:47 PM. Reason: Changing the title
Instructor
Joined: Jul 2020
Posts: 226
Likes: 43
From: New Jersey
So I have a 1985 C4 with 110k on the books, she idles really rough, by that I mean it jumps around like crazy all the way down to 370rpm is the lowest we’ve recorded. When I go to give it gas it stalls out and dies, when it does run on the highway I’m getting a lot of misfires as in I can hear the pops in the exhaust from it. My oil pressure sensor is reading 80 on a cold start. Whenever I go to give it gas on the highway it builds up a lot of power but doesn’t send it anywhere the engine only gets louder and when I let my foot off the gas the car shoots forwards. I’ve replaced the fuel filter, spark plugs, and air filter so far, what else could I need to get her back to life.
Thread Starter
6th Gear
Joined: Apr 2021
Posts: 6
Likes: 0
Does the service engine light come on during any of this? If so, you'd want to pull the codes and start troubleshooting from there. It sounds like the mixture is somehow dramatically wrong. My first guess would be that it's likely one of the sensors giving a bad reading and causing the computer to set the air-fuel mixture incorrectly. Maybe take a look at the connections/condition of things like the throttle position sensor, MAP sensor, coolant temperature sensor, etc.
Thread Starter
6th Gear
Joined: Apr 2021
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Instructor
Joined: Jul 2020
Posts: 226
Likes: 43
From: New Jersey
Thread Starter
6th Gear
Joined: Apr 2021
Posts: 6
Likes: 0
I think the oil temperature sensor is just used to calculate the oil life / oil change indicator - not to adjust mixture. Others like the MAP/MAF, Coolant Temperature, Intake Air Temperature, Throttle Position sensor, etc. will affect mixture and could cause the engine to run poorly or not at all. Do you have an ALDL cable you could connect and log data?
Instructor
Joined: Jul 2020
Posts: 226
Likes: 43
From: New Jersey
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